Author

Sebastian Zeki

Published

July 23, 2018

Modified

March 23, 2024

There are many occasions when a column of data needs to be created from an already existing column for ease of data manipulation. For example, perhaps you have a body of text as a pathology report and you want to extract all the reports where the diagnosis is ‘dysplasia’.

You could just subset the data using grepl so that you only get the reports that mention this word…but what if the data needs to be cleaned prior to subsetting like excluding reports where the diagnosis is normal but the phrase ‘No evidence of dysplasia’ is present. Or perhaps there are other manipulations needed prior to subsetting.

This is where data accordionisation is useful. This simply means the creation of data from (usually) a column into another column in the same dataframe.

The neatest way to do this is with the mutate function from the {dplyr} package which is devoted to data cleaning. There are also other ways which I will demonstrate at the end.

The input data here will be an endoscopy data set:

Age <- sample(1:100, 130, replace = TRUE)
Dx <- sample(c("NDBE", "LGD", "HGD", "IMC"), 130, replace = TRUE)
TimeOfEndoscopy <- sample(1:60, 130, replace = TRUE)

library(dplyr)

EMRdf <- data.frame(Age, Dx, TimeOfEndoscopy, stringsAsFactors = F)

Perhaps you need to calculate the number of hours spent doing each endoscopy rather than the number of minutes

EMRdftbb <- EMRdf %>% mutate(TimeOfEndoscopy / 60)

# install.packages("knitr")
library(knitr)
library(kableExtra)

# Just show the top 20 results

kable(head(EMRdftbb, 20))
Age Dx TimeOfEndoscopy TimeOfEndoscopy/60
87 NDBE 24 0.4000000
41 NDBE 48 0.8000000
15 LGD 40 0.6666667
16 HGD 19 0.3166667
38 IMC 22 0.3666667
87 IMC 52 0.8666667
29 HGD 55 0.9166667
20 IMC 45 0.7500000
83 NDBE 45 0.7500000
97 HGD 22 0.3666667
17 NDBE 50 0.8333333
81 NDBE 16 0.2666667
39 NDBE 40 0.6666667
43 HGD 34 0.5666667
12 IMC 56 0.9333333
62 NDBE 11 0.1833333
68 LGD 51 0.8500000
37 LGD 35 0.5833333
92 LGD 7 0.1166667
38 IMC 57 0.9500000

That is useful but what if you want to classify the amount of time spent doing each endoscopy as follows: <0.4 hours is too little time and >0.4 hours is too long.

Using ifelse() with mutate for conditional accordionisation.

For this we would use ifelse(). However this can be combined with mutate() so that the result gets put in another column as follows

EMRdf2 <- EMRdf %>%
  mutate(TimeInHours = TimeOfEndoscopy / 60) %>%
  mutate(TimeClassification = ifelse(TimeInHours > 0.4, "Too Long", "Too Short"))

# Just show the top 20 results

kable(head(EMRdf2, 20))
Age Dx TimeOfEndoscopy TimeInHours TimeClassification
87 NDBE 24 0.4000000 Too Short
41 NDBE 48 0.8000000 Too Long
15 LGD 40 0.6666667 Too Long
16 HGD 19 0.3166667 Too Short
38 IMC 22 0.3666667 Too Short
87 IMC 52 0.8666667 Too Long
29 HGD 55 0.9166667 Too Long
20 IMC 45 0.7500000 Too Long
83 NDBE 45 0.7500000 Too Long
97 HGD 22 0.3666667 Too Short
17 NDBE 50 0.8333333 Too Long
81 NDBE 16 0.2666667 Too Short
39 NDBE 40 0.6666667 Too Long
43 HGD 34 0.5666667 Too Long
12 IMC 56 0.9333333 Too Long
62 NDBE 11 0.1833333 Too Short
68 LGD 51 0.8500000 Too Long
37 LGD 35 0.5833333 Too Long
92 LGD 7 0.1166667 Too Short
38 IMC 57 0.9500000 Too Long

Note how we can chain the mutate() function together.

Using multiple ifelse()

What if we want to get more complex and put several classifiers in? We just use more ifelse’s:

EMRdf2 <- EMRdf %>%
  mutate(TimeInHours = TimeOfEndoscopy / 60) %>%
  mutate(TimeClassification = ifelse(TimeInHours > 0.8, "Too Long", ifelse(TimeInHours < 0.5, "Too Short", ifelse(TimeInHours >= 0.5 & TimeInHours <= 0.8, "Just Right", "N"))))

# Just show the top 20 results

kable(head(EMRdf2, 20))
Age Dx TimeOfEndoscopy TimeInHours TimeClassification
87 NDBE 24 0.4000000 Too Short
41 NDBE 48 0.8000000 Just Right
15 LGD 40 0.6666667 Just Right
16 HGD 19 0.3166667 Too Short
38 IMC 22 0.3666667 Too Short
87 IMC 52 0.8666667 Too Long
29 HGD 55 0.9166667 Too Long
20 IMC 45 0.7500000 Just Right
83 NDBE 45 0.7500000 Just Right
97 HGD 22 0.3666667 Too Short
17 NDBE 50 0.8333333 Too Long
81 NDBE 16 0.2666667 Too Short
39 NDBE 40 0.6666667 Just Right
43 HGD 34 0.5666667 Just Right
12 IMC 56 0.9333333 Too Long
62 NDBE 11 0.1833333 Too Short
68 LGD 51 0.8500000 Too Long
37 LGD 35 0.5833333 Just Right
92 LGD 7 0.1166667 Too Short
38 IMC 57 0.9500000 Too Long

Using multiple ifelse() with grepl() or string_extract

Of course we need to extract information from text as well as numeric data. We can do this using grepl() or string_extract() from the library(stringr).

Let’s say we want to extract all the samples that had IMC. We don’t want to subset the data, just extract IMC into a column that says IMC and the rest say ’Non-IMC’

Using the dataset above:

library(stringr)

EMRdf$MyIMC_Column <- str_extract(EMRdf$Dx, "IMC")

# to fill the NA's we would do:EMRdf$MyIMC_Column<-ifelse(grepl("IMC",EMRdf$Dx),"IMC","NoIMC")

# Another way to do this (really should be for more complex examples when you want to extract the entire contents of the cell that has the match)

EMRdf$MyIMC_Column <- ifelse(grepl("IMC", EMRdf$Dx), str_extract(EMRdf$Dx, "IMC"), "NoIMC")

So data can be usefully created from data for further analysis.

Hopefully this way of extrapolating data and especially using conditional expressions to categorise data according to some rules is a helpful way to get more out of your data.

Please follow @gastroDS on twitter

This article originally appeared on https://sebastiz.github.io/gastrodatascience/ and has been edited to render in Quarto and had NHS-R styles applied.

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For attribution, please cite this work as:
Zeki, Sebastian. 2018. “How to Extrapolate Data from Data.” July 23, 2018. https://nhs-r-community.github.io/nhs-r-community//blog/how-to-extrapolate-data-from-data.html.